7 notebooks cost $9.24. Which equation would help determine the cost of 3 notebooks?
Answer: There are several equations that could help determine the cost, each with a slightly different approach. We can write the fact that 7 notebooks cost $9.24 as a proportion: $\dfrac{7}{\$9.24}$ Let $x$ represent the unknown cost of 3 notebooks. Since 3 notebooks cost $x$ , we have the following proportion: $\dfrac{3}{x}$ The cost changes along with the number of notebooks purchased, and so the two proportions are equivalent. $\dfrac{7}{\$9.24} = \dfrac{3}{x}$